1. Field of the Invention
This invention relates generally to a medical device. More specifically, the invention relates to a balloon catheter that is convertible from an over-the-wire catheter (OTW) to a rapid-exchange (RX) catheter.
2. Background of the Invention
Cardiovascular disease, including atherosclerosis, is the leading cause of death in the U.S. The medical community has developed a number of methods and devices for treating coronary heart disease, some of which are specifically designed to treat the complications resulting from atherosclerosis and other forms of coronary arterial narrowing.
One method for treating atherosclerosis and other forms of coronary narrowing is percutaneous transluminal coronary angioplasty, commonly referred to as “angioplasty” or “PTCA”. The objective in angioplasty is to enlarge the lumen of the affected coronary artery by radial hydraulic expansion. The procedure is accomplished by inflating a balloon of a balloon catheter within the narrowed lumen of the coronary artery. Radial expansion of the coronary artery occurs in several different dimensions, and is related to the nature of the plaque. Soft, fatty plaque deposits are flattened by the balloon, while hardened deposits are cracked and split to enlarge the lumen. The wall of the artery itself is also stretched when the balloon is inflated.
One or multiple dilations may be necessary to effectively dilate the artery. In many instances, successive dilations using a succession of balloon catheters with balloons of increasingly larger diameters may be required. In order to accomplish the multiple dilations, the original catheter must be removed and a second balloon catheter tracked to the lesion.
There are several types of catheters presently available for performing the above-mentioned procedure. The two types of catheters most often used are referred to as over-the-wire (OTW) catheters and rapid exchange (RX) catheters. An OTW catheter has a guide wire lumen, which runs the entire length of the catheter. A RX catheter, on the other hand, has a guide wire lumen that runs for only the distalmost portion of the catheter.
To remove an OTW catheter, an extension must be placed on the original guide wire and multiple operators are required to hold the extended guide wire in place while the original catheter is changed out.
A RX catheter avoids the need for multiple operators when changing out the catheter and therefore is often referred to as a “single operator” catheter. With a rapid exchange catheter, the guide wire is outside the shaft of the catheter for all but the distalmost portion of the catheter. The guide wire can be held in place without an extension when the catheter is removed from the body. Once the original catheter is removed, a subsequent RX catheter may be threaded onto the in-place guide wire and tracked to the lesion.
However, there are instances when the guide wire and not the catheter must be replaced. For example, the guide wire may become damaged during the procedure or it may be discovered during the procedure that a different shape, length, or size of guide wire is needed. An OTW catheter, with the guide wire lumen extending the entire length of the catheter, allows for simple guide wire exchange. With a RX catheter, the guide wire lumen does not extend the entire length of the catheter. Therefore, the guide wire, and most of the catheter, must be removed from the body in order to exchange guide wires. Essentially the procedure must then start anew because both the guide wire and the catheter must be retracked to the lesion.
The choice of whether an OTW or RX catheter is best for a given procedure often depends upon the specifics of the procedure and often arises in real time of the procedure. For example, if a procedure requires multiple balloons to effectuate proper dilation, a RX catheter, allowing easy exchange of catheters, would be the preferred choice. But, if a procedure requires a change of guide wires, which in clinical practice is common, an OTW catheter is particularly advantageous because it gives a practitioner the ability to do so without changing catheters. Therefore, a balloon catheter capable of use as both an OTW and a RX catheter within the same procedure is particularly advantageous.
There are existing catheters that disclose universal mode designs, i.e., a design for use as either an OTW or RX catheter. For instance, an OTW catheter has been designed with a means for removing the catheter without the need for an extension to the guide wire. Essentially, a slit the length of the outer shaft of the catheter allows an operator to remove the guide wire from the catheter by holding the guide wire in place, and “peeling away” the catheter as the guide wire moves through the slit thereof.
However, this design does not allow the catheter to be used as both a RX catheter and an OTW catheter because by tearing away the catheter outer wall to expose the guide wire inside, the catheter is essentially destroyed. Back loading a subsequent guide wire once the catheter outer wall has been peeled away would be difficult if not impossible because the outer wall would no longer contain the guide wire.
Additionally, a catheter designed to eliminate the need for guide wire extensions or exchange wires is disclosed in U.S. Pat. No. 4,988,356, incorporated herein by reference (Crittenden, et al.). This “zipper-type” catheter includes a catheter shaft having a cut that extends longitudinally between the proximal end and the distal end of the catheter and that extends radially from the catheter shaft outer surface to the guide wire lumen. A guide member slidably coupled to the catheter shaft functions to open the cut such that the guide wire may extend transversely into or out of the cut at any location along its length. By moving the guide member, the effective over-the-wire length of the zipper-type catheter is adjustable.
When using the zipper-type catheter, the guide wire is maneuvered through the patient's vascular system such that the distal end of the guide wire is positioned across the treatment site. With the guide member positioned near the distal end of the catheter, the proximal end of the guide wire is threaded into the guide wire lumen opening at the distal end of the catheter and through the guide member such that the proximal end of the guide wire protrudes out the proximal end of the guide wire member. By securing the guide member and the proximal end of the guide wire in a fixed position, the catheter may then be transported over the guide wire by advancing the catheter toward the guide member. In doing so, the catheter advances through the guide member such that the guide wire lumen envelops the guide wire as the catheter is advanced into the patient's vasculature. In a PTCA embodiment, the zipper-type catheter may be advanced over the guide wire in this manner until the distal end of the catheter having the dilatation balloon is positioned within the stenosis and essentially the entire length of the guide wire is encompassed within the guide wire lumen.
Furthermore, the indwelling zipper-type catheter may be exchanged with another catheter by reversing the operation described above. To this end, the indwelling catheter may be removed by withdrawing the proximal end of the catheter from the patient while holding the proximal end of the guide wire and the guide member in a fixed position. When the catheter has been withdrawn to the point where the distal end of the cut has reached the guide member, the distal portion of the catheter over the guide wire is of a sufficiently short length that the catheter may be drawn over the proximal end of the guide wire without releasing control of the guide wire or disturbing its position within the patient. After the catheter has been removed, another catheter of any type may be threaded onto the guide wire and advanced over the guide wire in the same manner described above with regard to the zipper-type catheter. The zipper-type catheter not only permits catheter exchange without the use of the very long exchange guide wire and without requiring withdrawal of the initially placed guide wire, but it also overcomes many of the other difficulties discussed in association with RX catheters.
Despite these advantages, original zipper-type catheters in accordance with U.S. Pat. No. 4,988,356 at times fail to adequately contain the guide wire within the guide wire lumen during normal operation. In particular, as the catheter was advanced over the guide wire, the catheter could bend or buckle such that the guide wire could protrude from the catheter shaft. If the guide wire protruded from the catheter shaft, it could subsequently become pinched, and the distal end of the guide wire could be pulled out of or pushed beyond the treatment site, thus complicating the procedure and requiring repositioning within the patient's vasculature. Bending or buckling of a zipper-type catheter could also occur proximal to the guide member, where the guide wire is absent from the guide wire lumen. Thus there arises the need for a balloon catheter that gives a practitioner the flexibility to use the catheter as both an OTW and/or a RX catheter within the same procedure. It is among the general objects of the invention to provide an improved device that overcomes the foregoing difficulties.
The convertible balloon catheter of the present invention, capable of use as an OTW and a RX catheter, is a dual lumen catheter and as such, contains both a full-length guide wire lumen and an inflation lumen. The guide wire lumen must be large enough to allow the guide wire to pass through unimpeded. However, the guide wire lumen can not be so sized that the dual lumen catheter results in an unacceptable increase in the outer diameter of the catheter shaft. There arises a need to maintain a small overall outer diameter for the convertible catheter but not decrease the size of the guide wire lumen to the point that resistance between the catheter and the guide wire is adversely affected. The convertible catheter of the present invention includes a collapsible inflation lumen, which can be any shape, for example crescent-shaped, “D”-shaped, or circular. During insertion of the guide wire into the guide wire lumen, the inflation lumen is collapsible which allows for an increase in the dimensions of the guide wire lumen. The enlarged guide wire lumen eases tracking of the catheter over the guide wire.
Assembling balloon catheters is a process that requires the intricate steps of attaching the various parts of the catheters. Each component of the catheter is attached to the others by hand, often in an assembly-line type setting. The components of angioplasty catheters are relatively small and not easily attached to the others. Tack welding and glueing the component parts can be a very difficult task. Each step presents the chance that human error will lead to a faulty product. Thus there arises the need to minimize the number of components of the balloon catheter to minimize the number of steps necessary to assemble the catheter.
For the present invention, the general method of manufacture could be as follows: an extruded, or blown, thin-walled tube (inner shaft) is placed into, for example, a discretely extruded tapered shaft (outer shaft). Using a CO laser, for example, the inner shaft is tack welded to the inner surface of the outer shaft. A much longer tack weld is applied at the distal-most end of the inner shaft after which one or more small holes are formed through the outer shaft, tack weld, and inner shaft. Again the holes are formed by laser or another method, to allow access from the inflation lumen to the balloon. The balloon can be positioned onto the distal-most portion of the outer shaft and laser-welded, glued or attached via a suitable method. The distal-most tip of the catheter can be profiled either mechanically, e.g., sanding, by laser or another suitable heating method. The removable hatch is formed by creating a multitude of small, relatively weak points or preforations in a predetermined pattern at one or more locations in the outer shaft. At the proximal end of the catheter, a molded hub can be for example over-molded or ultrasonically welded onto the shaft assembly.
Accordingly, there is a need for a convertible catheter that can be used as either an OTW or RX catheter, a convertible catheter with a reduced outer diameter, and a simplified method of manufacture.